Motion video signals typically contain a significant amount of spatial and temporal redundancy. Video compression techniques take advantage of such spatial and temporal redundancy to reduce the amount of data bandwidth required to process, transmit and store video signals. MPEG-2 is a well-known video compression standard developed by the International Standards Organization (ISO) Moving Picture Experts Group (MPEG) and documented in “Information Technology Generic Coding of Moving Pictures and Associated Audio Information: Video,” ISO/IEC DIS 13818-2 (Video), which is incorporated herein by reference. MPEG-2 video compression involves both spatial and temporal compression of video frames or fields. Other video standards, such as AVC 14496-10 and HEVC, also call for video compression techniques that involve both spatial and temporal compression of video frames or fields.
A digital video encoder is a component which converts digital video from one format to another for the purposes of standardization, speed, secrecy, security, and/or compression. A digital video encoder may receive a sequence of video frames or fields from a video source. Spatial compression may be applied to the video frames by the digital video encoder using the techniques of transform encoding, quantization, scanning, run-amplitude encoding and variable length coding for example. Temporal compression may be applied to the video frames by the digital video encoder using the techniques of motion estimation and motion compensation as an example.
Video preprocessing (also known as pre-filtering) techniques are applied prior to performing spatial and temporal compression. A digital video preprocessor is a component that processes a digital video signal using one or more preprocessing filters so that the digital video may be more efficiently compressed by subsequent video compression components, such as a digital video encoder. For example, the digital video preprocessor may alter the format of each frame in terms of the number of horizontal or vertical pixels in order to meet parameters specified by a video compression component. In addition, a digital video preprocessor may detect and beneficially inform a video compression component of certain scene changes and/or other image variations (such as a fade) in the digital video which increase compression difficulty.
Conventional video preprocessing techniques have generally been concerned with detecting and correcting obvious problematic situations in the visible content of the digital video, such as format alterations, scene changes and fades.